JP3087924B2 - Method of manufacturing piezoelectric ceramic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention _is, PbTiO 3 -PbZ
The present invention relates to a method for manufacturing an rO ₃ (hereinafter, referred to as PZT) piezoelectric ceramic. The piezoelectric ceramic manufactured according to the present invention can be used for a piezoelectric actuator for an automobile which requires particularly high mechanical strength.

[0002]

2. Description of the Related Art PZT piezoelectric ceramics exhibit excellent piezoelectric characteristics and are widely used as piezoelectric actuators.
In order to manufacture this PZT-based piezoelectric ceramic, first, a raw material powder mainly composed of PbO, TiO ₂ and ZrO ₂ is mixed by a ball mill or the like. The mixed powder is calcined to form a PZT powder, and after pulverization, a compact having a predetermined shape is formed. And
It is a general method to sinter the molded body and then perform post-processing such as machining or polarization to form a piezoelectric ceramic.

When a PZT piezoelectric ceramic is used as a piezoelectric actuator, it is desirable that the piezoelectric characteristics be good, that is, the piezoelectric distortion constant (d ₃₃ ) be large. When used as parts of automobiles, the operating temperature is 10
Since the temperature is around 0 ° C., the Curie temperature (Tc) is desirably 180 ° C. or higher in order to prevent polarization deterioration. It has been found that the piezoelectric strain constant and the Curie temperature vary greatly depending on the type of metal element constituting the piezoelectric ceramic and its composition ratio.

For example, when Nb is added to a PZT-based solid solution,
It is known that the dielectric constant of the K constant increases, and the piezoelectric strain constant increases accordingly. It is also known that replacing Pb with Sr increases the dielectric constant.
Further, JP-A-2-288381 discloses a formula (Pb
_{1-x Sr x) (Zr} y Ti 1-yz Nb z) O 3 wherein
0.08 ≦ x ≦ 0.14, 0.49 ≦ y−0.5 x ≦ 0.51, 0.005 ≦ z
≦ 0.02], 400 × 10
A piezoelectric ceramic composition that can achieve a piezoelectric strain constant of ⁻¹² m / V or more and a Curie temperature of 200 ° C. or more is disclosed.

[0005] In recent years, the range of use of PZT-based piezoelectric ceramics has been expanded, and the use of PZT-based piezoelectric ceramics in automobile engine control parts such as fuel injectors has been studied. However, when it is used for such a part, it can be used under high temperature conditions.
Since a load of 0 to 400 kg is applied, driving durability is a major problem. In order to improve the driving durability,
It is necessary to provide a piezoelectric ceramic having a high Curie temperature and high strength.

It is known that two methods are effective as methods for improving the strength of a ceramic sintered body: a method for improving the sintered density, and a method for reinforcing grain boundaries by mixing Al, Si or the like. I have. However, in piezoelectric ceramics, the type of material to be mixed, its state, mixing method, dispersion state, and the like have a great effect on the piezoelectric characteristics, and therefore the latter method cannot be used. Therefore, as the former method,
As disclosed in JP-A-9352 and JP-A-63-100075, a method of hot isostatic pressing of a compact in a high-temperature and high-pressure gas atmosphere (hereinafter referred to as HIP treatment) may be useful. Are known. According to this HIP processing method, since there is no limitation on the pressing force and size as compared with the hot press method and the like, and no impurities are mixed from the container or the pressure medium, the HIP processing method is excellent in quality and productivity, and the sintering density easily Can be improved.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Laid-Open No.
In the piezoelectric ceramic composition disclosed in JP-A-288381,
Although the piezoelectric strain constant and Curie temperature are satisfactory, HI
Even when manufactured using the P treatment method, dissatisfaction in strength was left. The present invention has been made in view of such circumstances, and it is an object of the present invention to maintain the piezoelectric distortion constant and the Curie temperature at almost the same high values as in the past, and further improve the transverse rupture strength representing the strength. I do.

[0008]

A method for manufacturing a piezoelectric ceramic according to the present invention for solving the above-mentioned problems is represented by the formula (Pb _1-x Sr _x ) (Z
_{r y Ti 1-yz Nb z} ) O 3 wherein, 0.08 ≦ x ≦ 0.14,
0.49 ≦ y−0.5 x ≦ 0.51, 0.02 <z ≦ 0.06], a molding step of forming a molded body of a predetermined shape from the raw material powder prepared so as to have a composition represented by: And a HIP processing step of sintering the primary sintered body under a high temperature and high pressure gas.

The present inventors have conducted intensive studies to improve the transverse rupture strength of the composition disclosed in JP-A-2-288381. The inventors have found that the sintering and the subsequent HIP treatment significantly improve the transverse rupture strength of the obtained piezoelectric ceramic, and completed the present invention. When the content of Nb is increased, the piezoelectric strain constant and the Curie temperature are decreased. Therefore, in the above publication, z ≦ 0.02. However, as Nb increases, the piezoelectric strain constant and Curie temperature decrease,
It has been found that the degree of the decrease is small and in a sufficiently usable range, and the degree of improvement in the transverse rupture strength by appropriate sintering is much larger than that.

The reason why the composition ratio x of Sr is set to 0.08 ≦ x ≦ 0.14 is that if it is out of this range, the piezoelectric strain constant becomes 400 × 10
^This is because the Curie temperature becomes lower than 180 ° C. when it is lower than ⁻¹² m / V and higher than 0.14. The composition ratio y of Zr is 0.49 ≦ y−0.5 in relation to the composition ratio x of Sr.
It is necessary to satisfy x ≦ 0.51. If y-0.5x is out of this range, the piezoelectric strain constant and the bending strength become insufficient.

The composition ratio z of Nb is in the range of 0.02 <z ≦ 0.06. If z is less than 0.02, an increase in bending strength cannot be expected, and if it exceeds 0.06, the piezoelectric strain constant and Curie temperature become insufficient. The range of 0.03 ≦ z ≦ 0.05 is particularly preferred. P
The composition ratio of b, Sr, Zr, Ti and Nb is x, y, z
Is uniformly mixed and calcined. This calcination forms a PZT solid solution, and is generally performed at a temperature of 800 to 900 ° C. as in the prior art. The obtained PZT raw material powder is pulverized again by a ball mill or the like, and formed into a molded body in the same manner as in the related art.

In the primary sintering step, which is one of the features of the present invention, the compact is sintered so as to have a density lower than an ideal density. Here, the ideal density may be a theoretical density calculated from the concentration of each element in the obtained sintered body, or a concept including the actually obtained maximum sintered density slightly lower than the theoretical density. It is preferable to perform sintering so as to have a density of 91% or more of the ideal density. The density of the primary sintered body is 91% of the ideal density
If it is less than the above, the effect of the HIP processing is reduced. This primary sintering step is preferably performed in a state of being buried in PZT raw material powder or the like in order to prevent volatilization of the lead component.

The second invention of the present application is most characterized in that the primary sintering step is performed in an oxygen-enriched state. By sintering in an oxygen-enriched state, the melting temperature of PbO is lowered, and sintering can be performed more densely. Then, since the inside of the pores in the primary sintered body is replaced with oxygen, oxygen is dissolved in the HIP treatment step, and the gas in the pores is reduced, so that the pores can be further reduced by the HIP treatment.

As the conditions of the primary sintering step, it is recommended that the sintering temperature is 1250 ± 50 ° C., the sintering time is 10 minutes to 5 hours, and the oxygen concentration is 50% or more. In the HIP processing step, the temperature is 1250 ± 50 ° C., the processing time is 10 minutes to 5 hours, the pressure is 100 to 200 MPa, and the heating rate is 200 to 500 ° C. /
It is desirable to carry out under the condition of hr.

As described above, the primary sintering step and the HI
By performing the P treatment step, the piezoelectric strain constant becomes 400 ×
It is possible to produce a piezoelectric ceramic having a Curie temperature of more than 10 ⁻¹² m / V, a Curie temperature of 180 ° C. or more, and a bending strength of 90 MPa or more.

[0016]

The raw material powder used in the production method of the first invention has a composition ratio z of Nb in the range of 0.02 <z ≦ 0.06,
Nb is contained more than before. Thereby, the grain size of the piezoelectric ceramic crystal becomes small. For example, Nb is 1 mol%
In this case, the average particle size is about 10 μm and the density is 95%, but it is clear that when Nb is 4 mol%, the average particle size is reduced to about 2 μm and the density is improved to 99%. Therefore, the diameter of the holes generated inside the piezoelectric ceramic is reduced, and the bending strength is improved.

By increasing the composition ratio of Nb, the piezoelectric strain constant and the Curie temperature decrease, but when z is 0.06 or less, the degree of decrease in the piezoelectric strain constant and the Curie temperature is small, and the piezoelectric material is sufficiently used for automobile parts. It is in the possible range. Then, since the primary sintering and the HIP treatment are performed using the raw material powder in which Nb is increased, the pores are further reduced and the density is improved. Furthermore, if the primary sintering step is performed in an oxygen-enriched state, the sintered body can be densely sintered by lowering the melting temperature of PbO, and the oxygen gas is solid-dissolved in the peripheral wall in the void replaced by the oxygen gas. The amount of gas in the inside is reduced, and the compression of the pore volume during the HIP process is promoted, so that a more dense sintered body can be obtained.

[0018]

Hereinafter, the present invention will be described in detail with reference to test examples. (1) Test Example 1: ratio of components considered the main component of the composition ratio of Nb has the formula _{(Pb 1-x Sr x)} (Zr y Ti
_1-yz Nb _z ) When represented by O ₃ , x = 0.11, y =
It is fixed at 0.55, z is selected in the range of 0.005 ≦ z ≦ 0.07, and lead oxide (PbO), zirconium oxide (Zr
O ₂ ), titanium oxide (TiO ₂ ) and niobium pentoxide (N
b ₂ O ₅ ) powder was prepared and wet-mixed in a ball mill for 48 hours. After dehydration and drying, this was calcined in air at 800 ° C. for 5 hours. Thereafter, wet grinding was performed again in a ball mill for 48 hours, followed by dehydration and drying.

The obtained mixed powder is granulated by adding 1% by weight of polyvinyl alcohol (PVA) as a binder, and is granulated at a molding pressure of 1000 kg / cm ² and a diameter of 20 mm and a thickness of 1 m.
m was formed into a disk-shaped molded body. Each of the obtained compacts was fired at 1250 ° C. for 1 hour in the atmosphere to obtain piezoelectric ceramics having different Nb contents.

Each piezoelectric ceramic has two
A silver electrode is formed, and a voltage of 1 KV / cm is applied.
Perform polarization treatment for 30 minutes in silicone oil at 00 ° C
Was. After standing for 24 hours, each piezoelectric ceramic
And the piezoelectric strain constant (d₃₃), Curie temperature and flexural strength
It was measured. The results are shown in FIGS. Piezoelectric distortion constant (d
₃₃) Turns off the voltage applied to the piezoelectric ceramic at 0V and 500V.
And measure the distortion of the piezoelectric ceramic directly with a surface roughness meter.
I asked. The Curie temperature is calculated from the temperature change of the dielectric constant.
Was. The bending strength is measured with a 10 mm span jig.
It was obtained by bending the porcelain as it was.

[0021] From FIG. 1 and FIG. 2, d ₃₃ and a Curie temperature as the content of Nb is increased it can be seen that the decrease. However, the content of Nb is 6 mol% or less (z ≦ 0.06)
Then, the piezoelectric strain constant (d ₃₃ ) is 400 × 10 ⁻¹² m
/ V or more, and the Curie temperature is 180 ° C. or more, which is in a sufficiently usable range. On the other hand, from FIG.
When the content exceeds 2 mol% (0.02 <z), it is apparent that the transverse rupture strength is remarkably increased. is there. (2) Test Example 2: Examination of composition ratio of components other than Nb Next, the content of Nb was fixed to 4 mol% (z = 0.04),
Substituting 6-16 mol% of Pb with Sr, Zr / (Zr + T
i) changed in the range of 0.51 to 0.60 (x = 0.06 to
0.16, y = 0.51-0.60). The composition of each prepared powder is shown in FIG. 4 by circled numbers. Note that strontium carbonate (SrCO ₃ ) was used as the Sr source. Each piezoelectric ceramic was produced in the same manner as in Test Example 1, and the piezoelectric strain constant (d ₃₃ ), Curie temperature, and bending strength were measured in the same manner. Table 1 shows the results.

According to Table 1, the piezoelectric strain constant (d ₃₃ ) is 400
× 10 ⁻¹² m / V or more, Curie temperature of 180 ° C. or more,
Further, when a material having a transverse rupture strength of 80 MPa or more was selected and displayed in FIG. 4, the hatched area in FIG. 4 was obtained. When this shaded area is represented by a mathematical expression using x and y, 0.08 ≦ x ≦ 0.14 and 0.
49 ≦ y−0.5 x ≦ 0.51. That is, the equation (Pb _1-x
Z In _{Sr x) (Zr y Ti 1} -yz Nb z) O 3 Formula
Is 0.04, 0.08 ≦ x ≦ 0.14 and 0.49 ≦ y−0.5 x
If ≦ 0.51, it can be seen that a high bending strength is obtained while maintaining the piezoelectric strain constant (d ₃₃ ) and the Curie temperature in the optimum ranges, and it is optimum as an actuator material.

[0023]

[Table 1]

(3) Test Example 3: Examination of Sintering Conditions (Part 1) Therefore, each of the compacts formed in Test Example 1 was first subjected to primary sintering by heating at 1250 ° C. for 1 hour in the air, and then Using a gas having a mixture ratio of O ₂ / Ar = 1/5, HIP treatment was performed at a heating rate of 400 ° C./hr under a pressure of 100 MPa and holding at 1250 ° C. for 1 hour.

For each of the obtained piezoelectric ceramics, the piezoelectric strain constant (d ₃₃ ), the Curie temperature and the bending strength were measured. With respect to the piezoelectric strain constant (d ₃₃ ) and the Curie temperature, almost the same results as those obtained in Test Example 1 were obtained. On the other hand, it was revealed that the transverse rupture strength was further improved as compared with Test Example 1 as shown in FIG. (4) Test Example 4: Examination of Sintering Conditions (Part 2) Each of the compacts formed in Test Example 1 was subjected to PbZrO
₃ was placed in an alumina crucible and heated at 1250 ° C. for 1 hour in a sintering furnace while a constant amount of 100% oxygen gas was introduced, while maintaining a PbO atmosphere, to perform primary sintering.

The obtained primary sintered body was subjected to the HIP treatment in the same manner as in Test Example 3 to obtain each piezoelectric ceramic. For each of the obtained piezoelectric ceramics, the piezoelectric strain constant (d ₃₃ ), the Curie temperature, and the bending strength were measured. With respect to the piezoelectric strain constant (d ₃₃ ) and the Curie temperature, almost the same results as those obtained in Test Example 1 were obtained. On the other hand, it became clear that the transverse rupture strength was remarkably improved as compared with Test Examples 1 and 3 as shown in FIG.

The piezoelectric ceramics obtained by primary sintering each of the molded bodies formed in Test Example 2 in an oxygen atmosphere in the same manner as described above and then performing HIP treatment were used to obtain a piezoelectric strain constant (d ₃₃ ), The Curie temperature and flexural strength were measured, and the results are shown in Table 2. From Table 2, the piezoelectric strain constant (d ₃₃ ) is 40
0 × 10 ^-12 m / V or more, a Curie temperature of 180 ° C. or higher, further bending strength Selecting more than 110 MPa, the hatched area similar to that of FIG. 4 is obtained.

That is, in the method of performing primary sintering in an oxygen atmosphere and further performing HIP treatment, the formula (Pb _1-x Sr
_{x) (Zr y Ti 1-} yz Nb z) at O ₃ formula z is 0.
At the time of 04, 0.08 ≦ x ≦ 0.14 and 0.49 ≦ y−0.5 x ≦ 0.
With the composition of 51, the bending strength is 11 while maintaining the piezoelectric strain constant (d ₃₃ ) and the Curie temperature in the optimum ranges.
It is clear that the improvement is remarkably increased to 0 MPa or more.

[0029]

[Table 2]

(5) Test Example 5: Durability of Piezoelectric Characteristics A composition having a Nb content of 5 mol% was selected in Test Example 1, and a piezoelectric ceramic obtained by the method of Test Example 1 (without HIP treatment)
And a piezoelectric ceramic (HIP treatment after sintering in oxygen) obtained by the method of Test Example 4 was subjected to a durability test in which a load of 300 kgf was applied, and a voltage of −100 to 600 V was repeatedly applied at an ambient temperature of 100 ° C. Was. Then, the piezoelectric strain constant (d ₃₃ ) during the durability test was measured, and the results are shown in FIG.

FIG. 5 shows that the piezoelectric strain constant decreases as the durability test progresses. This is because the polarization direction of the piezoelectric ceramic is shifted from the strain direction (polarization direction) due to the applied voltage, load, and temperature, that is, 90-degree domain switching frequently occurs. FIG. 5 shows that the piezoelectric ceramic obtained by the method of Test Example 4 has a smaller degree of reduction than the conventional one. This is because the distortion of the crystal lattice repeatedly acts between the domains during the 90-degree domain switching, which may cause a fine crack. However, the higher the strength, the smaller the possibility of the occurrence of the fine crack. It is thought. (6) Test Example 6: Retention Ratio of Piezoelectric Strain Constant The two types of piezoelectric ceramics of Test Example 5 and the piezoelectric ceramics obtained by the method of Test Example 1 with the composition of Test Example 1 having a Nb content of 1 mol%. for (HIP without treatment), and the initial anti拆強of the piezoelectric ceramic was calculated retention of piezoelectric strain constant of a piezoelectric strain constant before and after the durability test described above was repeated durability test 10 ⁸ times. FIG. 6 shows the results. From FIG. 6, there is a correlation between the initial bending strength and the retention rate of the piezoelectric strain constant,
It can be seen that the higher the initial bending strength, the higher the retention of the piezoelectric strain constant. That is, conventionally, a decrease in the piezoelectric strain constant was considered to be an electrical characteristic. From this result, it has been clarified that a decrease in the piezoelectric strain constant can be prevented by increasing the bending strength.

[0032]

According to the method for manufacturing a piezoelectric ceramic of the present invention, a piezoelectric ceramic having a significantly higher bending strength than conventional ones can be obtained while maintaining a high piezoelectric strain constant and Curie temperature. Therefore, the obtained piezoelectric ceramic is hardly cracked even under high temperature and high load, and is particularly suitable for a piezoelectric actuator for automobile parts.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of Nb added and the piezoelectric strain constant (d ₃₃ ).

FIG. 2 is a graph showing the relationship between the amount of Nb added and the Curie temperature.

FIG. 3 is a graph showing the relationship between the amount of Nb added and bending strength.

FIG. 4 is a graph illustrating an optimal range of an x value and a y value.

FIG. 5 is a graph showing the relationship between the number of endurance tests and the piezoelectric strain constant.

FIG. 6 is a graph showing a relationship between a bending strength and a holding ratio of a piezoelectric strain constant.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/49 C04B 35/64 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] 1. The formula (Pb _1-x Sr _x ) (Zr _y Ti
_1-yz Nb _z ) O ₃ [wherein 0.08 ≦ x ≦ 0.14, 0.49 ≦ y
−0.5 x ≦ 0.51, 0.02 <z ≦ 0.06], a forming step of forming a molded body of a predetermined shape from the raw material powder prepared so as to have a composition represented by the following formula, and sintering the molded body at a predetermined temperature. A method for manufacturing a piezoelectric ceramic, comprising: a primary sintering step of forming a primary sintered body; and a HIP processing step of sintering the primary sintered body under a high-temperature and high-pressure gas. 2. The formula (Pb _1-x Sr _x ) (Zr _y Ti
_1-yz Nb _z ) O ₃ [wherein 0.08 ≦ x ≦ 0.14, 0.49 ≦ y
−0.5 x ≦ 0.51, 0.005 ≦ z ≦ 0.06], a molding step of forming a molded body of a predetermined shape from the raw material powder prepared so as to have a composition represented by the following formula: A primary sintering step of sintering the enriched state at a predetermined temperature to obtain a primary sintered body, and a HIP treatment step of sintering the primary sintered body under a high-temperature and high-pressure gas. Manufacturing method of piezoelectric ceramic.